In electrostatographic reproduction, a light image of an original to be printed is typically recorded in the form of a latent electrostatic image upon a photosensitive member with a subsequent rendering of the latent image visible by the application of electroscopic marking particles, commonly referred to as toner. The visual toner image can be either fixed directly upon the photosensitive member or transferred from the member to another support medium such as a sheet of plain paper. To render this toner image permanent, the image must be “fixed” or “fused” to the paper, generally by the application of heat and pressure.
With the advent of high speed xerography reproduction machines wherein printers can produce at a rate in excess of three thousand copies per hour, the need for corotrons or dicorotrons at many processing stations is needed in a reliable and dependable manner in order to utilize the full capabilities of the reproduction machine. These corotron systems must operate flawlessly to virtually eliminate risk and generate minimum machine shutdowns due to corotron malfunctions.
Generally, in electrostatographic or electrostatic printing processes, a number of corotrons or dicorotrons are used at various stations around the photoreceptor. For example, the dicorotrons are used at the station that places a uniform charge on the photoreceptor, at a transfer station, at a cleaning station, etc. In today's high speed printers, it is important that all corotrons (or dicorotrons) are in perfect working order since one corotron malfunction can easily render the entire printing process useless. Some high speed printers including color printers use several dicorotron units. In one embodiment, as many as sixteen corotron or dicorotron units are used. So, maintaining each corotron or dicorotron unit in perfect working order is essential to the proper functioning of these complex fast color printers. It is common to use one or several corona-generating device(s) (“corotron” or “dicorotron”) for depositing the electrostatic at the above-noted stations. Generally, the structure of a dicorotron uses a thin, glass-coated wire mounted between two insulating anchors or end blocks called “anchors” which support the wire in a highly tensioned manner in a singular plane. In this disclosure, the term “anchors” includes insulator, end blocks, insulating anchors, etc. These anchors are installed between flexible holders or clamps or anchor inserts that maintain the anchors in place. These anchor inserts are fixed at two opposite ends of a U-shaped dicorotron “housing” or “shells” or “shield”. The wire or corona-generating electrode is typically a highly conductive elongated wire situated in close proximity to the photoconductive surface to be charged. Often, the corona discharge electrode is coated with a dielectric material such as glass, for glass coating improves charging uniformity throughout the electrode's life. Since the wire electrode is comprised of a thin outer glass brittle coating, it may be easily damaged. Some handling or cleaning of this electrode often results in fracture of the glass coating which could cut or injure the user. While cleaning sometimes corrects problems in this corona electrode, it is sometimes necessary to replace the wire due to degradation in the corona performance or even in breakage of the electrode which could occur during the cleaning.
Manual handling of the glass-coated wire is not recommended nor is the use of prying tools such as screw drivers or rigid prying objects. Extreme care needs to be observed in changing the corona electrodes or wires. As above noted, because of the large number of dicorotrons or wires needed in some copiers, malfunctioning of these wires presents a formidable problem in today's complex copiers.
Another important consideration is the high costs of dicorotron assemblies. The most expensive major component in the dicorotron assembly is the housing or U-shaped shield which houses the wire assembly and the wire anchors. The least expensive major component in the dicorotron assembly is the wire assembly. It makes sense, therefore, for the faulty wire assembly to be removed and replaced rather than the expensive entire dicorotron assembly made up of the wire assembly and U-shaped housing.
There are some systems used to remove and replace wire electrodes from the U-shaped housing such as the method disclosed in U.S. Pat. No. 5,449,906 (Osbourne). In this prior art system, the U-shaped housing has apertures on its end portions adjacent to the electrode anchors or insulators. A prying tool is then inserted into this aperture to pry or dislodge the two end insulators from their original position thereby removing the two insulators and the attached wire electrode. A tool for replacing the removed wire electron in Osbourne's process includes a plurality of replacement electrodes mounted on a rigid support frame. Replacement is accomplished by pressing this support frame containing a plurality of corona-generating wire assemblies against the empty U-shaped housing (where old wire has been removed) and thereby replacing the removed wire electrode with a new wire electrode. This prior art process requires prying or dislodging the old wire through an aperture and replacing the old wire with a mounting system where a plurality of corona- generating electrode assemblies are removably mounted in a configuration matching that of the original configuration.